1. Field
The present invention relates generally to gearboxes, and more particularly, to a universal two speed gearbox for driving drilling machines, digging and transport vehicles, and other devices which require variable operating two speed bearing thrust.
2. State of the Art
A number of gearboxes and transmission wheel hubs are known. For example, Buuck et al., U.S. Pat. No. 5,478,290 discloses a two speed high shift transmission residing within a rotatable wheel hub. It has dual hydraulic clutches to activate select gears of a planetary gear set including a first sun gear, a first planet gear, a first planet carrier and an inner ring gear. The first planet carrier includes a gear, which drives a second planetary gear set resulting in rotation of a wheel hub. When the first clutch is engaged, the inner ring gear is locked to a stationary outer ring effecting a high ratio reduction. When pressure to the first clutch is removed and applied to the second clutch, said first clutch disengages and said second clutch engages the sun gear and the planet carrier locking them together so that the sun gear, planet gear and planet carrier and inner ring gear rotate in unison effecting a low ratio reduction. Buuck et al may also incorporate a second planetary gear system operably associated with the hub to be selectively be engaged. The Buuck invention requires exterior dynamic seals, which are subject to leakage, and is subject to large clutch or brake forces exerted upon rotary bearings. This requires large design of the transmission and bearings to withstand such clutch and brake forces
Blanchard, U.S. Pat. No. 4,331,432 discloses a two speed automatic transmissions for marine propulsion. It employs an hydraulically actuated two speed transmission with a single fluid multi-pressure actuated clutch for activating different output shafts. (list any deficiencies or limitations in usage, etc.)
Brandt et al, U.S. Pat. No. 5,006,100 discloses a two-speed planetary gear mechanism employing an hydraulically actuated piston to activate the ring gear of a planetary gear system in either one or two directions. It does not employ a clutch for smoother operation.
Nelson, U.S. Pat. No. 6,350,165B1 discloses a marine stern drive two-speed automatic transmission employing a planetary gear apparatus including two hydraulic clutches and a ring gear brake to provide two forward drive ratios, a reverse ratio, or a neutral ratio. In another embodiment, a third hydraulic clutch is included with bevel gears alone to provide two forward and reverse speeds.
Legner, U.S. Pat. No. 5,509,860 discloses a power shift two-speed epicyclical gear box employing two hydraulically engaged friction clutches, which are alternatively engaged and disengaged by the force exerted by plate springs or hydraulic pistons. An accumulator and a check valve system are associated with the pressure chambers of the friction clutches to improved the shifting quality, particularly when downshifted from second to first gear.
Ahlen, U.S. Pat. No. 4,178,814 discloses a two-speed gear transmission employing a direct drive connectable clutch wherein the input and output shafts rotate together and a second gear drive namely overdrive or under drive have one of the sun or ring hears held stationary by a brake relative to the casing.
Co-applicant, Dusan Hvolka's co-pending filing with Strong et al. entitled “Two Speed Gearbox” discloses a two speed planetary gearbox activated by inboard and outboard clutches each associated with its own separate planetary gear system located and controlled in the wheel hub of the axle. In the low range, it employs a static clutch. In the high range it employs a dynamic clutch sealed with dynamic seals, which leak as the pressure increases; thereby requiring at high pressures a pump to remove excess fluids.
Other two speed shiftable gearboxes have short bearing lives when the two speed gearbox is operated for long periods of time in high range. This is because there is a large thrust load on the thrust bearing between the High Range Apply Piston and the High Clutch. All applications will be torque limited in the high range due to the limitations of the input horsepower. This results in a lower required input torque as the input speed to the box increases. Since the required thrust load through the bearing is directly proportional to the torque, and since the life of the bearing is a function of the thrust load, an increase bearing life will result from reducing the thrust load on the bearing
The invention described below provides an improved two speed gearbox activated with a non-rotating piston used to apply the force required to activate the high-speed clutch using a locking pin and a thrust bearing to allow the piston to secure the sun gear of a planetary gear system to remain in a high operating range, and a second low-speed clutch securing the ring gear of the planetary gear system in the low operating range.